As bridges age, they deteriorate due to traffic and corrosion or are subjected to loads exceeding those for which they were originally designed. This creates a need to repair or modify existing bridges. Also, growing traffic demands new bridges. The bridge's foundation supports the bridge's main structural members called the superstructure. The superstructure, in turn, supports the bridge deck upon which traffic moves. As the foundation and superstructure deteriorate, the load that the bridge can support is reduced. Reducing the bridge's deck weight reclaims traffic load capacity lost to that deterioration. The deck and superstructure of moveable bridges are periodically lifted to permit the passage of ships in the waterway spanned by the bridge. For such bridges, lightweight bridge decks that are weight neutral to steel open grid decks are needed.
Many moveable bridges use steel grating (a.k.a. steel open-grid deck or steel open-grid roadway flooring) for the bridge deck in an effort to reduce weight. Grating, however, has many disadvantages. It provides little skid resistance for vehicles, especially when worn. Drivers perceive a lack of control of their vehicles on the grating surface. Traffic is noisy when traversing grating. The grating and welds attaching the grating to the bridge superstructure are especially prone to fatigue failure. The openings in the grating permit moisture and debris to collect on the surfaces of the superstructure steel members, which promotes corrosion. Finally, grating permits liquids from vehicles to pass through the grating and below the bridge, polluting waterways.
In 2012, the Florida Department of Transportation (FDOT) published a report entitled Bascule Bridge Lightweight Solid Deck Retrofit Research Report—Deck Alternative Screening Report. (prepared by URS now AECOM)(hereinafter referred to as the “FDOT Report). The FDOT Report investigated and evaluated alternative deck systems that may be used to replace steel open-grid bridge decks for bascule bridges. To that end the report evaluated an aluminum orthotropic deck system. More specifically, the FDOT Report evaluated a friction-stir welded 5-inch aluminum orthotropic deck similar to the 8-inch deep Sapa R-Section Deck, but fabricated specifically to replace a 5-inch steel open-grid deck.
The alternative 5-inch deep aluminum orthotropic deck extrusion proposed in the FDOT is illustrated in FIG. 1. Again, the extrusion profile is similar to the 8-inch Sapa R-section deck extruded by Sapa Extrusions, Inc. As shown, the extrusion 200 includes a top flange 202, a bottom flange 204, inclined plates 206, 208 and a vertical plate 210 disposed between the inclined plates 206, 208 forming voids 212, 214 having a cross-sectional inverted right triangle configuration.
While the FDOT proposed the aluminum extrusion 200 of FIG. 1 as an option for a 5-inch aluminum orthotropic bridge deck panel, the inventors of the subject invention are not aware that such a bridge deck panel has been fabricated. However, the assignee, AlumaBridge, LLC, conducted fabrication trials with both the 5-inch and 8-inch deep orthotropic aluminum bridge deck panels having the extrusion profile as that of FIG. 1. The aluminum extrusions were longitudinally shop welded to form the bridge deck panels using a two-sided friction-stir welding with self-reacting pin tools. It was found that the fabrication of a bridge deck panels and a bridge deck using the extruded aluminum elements of FIG. 1 and friction-stir welding, was cost prohibitive.
Again in reference to FIG. 1, the respective ends 202A, 202B of the top flange 202 are relatively close to respective radii 216A, 216B between inclined plates 206, 208 and flange ends 202A, 202B. The top flange ends 202A, 202B were about 0.850 inches thick, and the bottom flanges 204 were about 0.370 inches thick. The lower pin tool of the friction-stir welding system tended to bounce during welding because the radii 216A, 216B were too close to the ends 202A, 202B creating difficulties in welding. More specifically, when welding top flanges of adjacent extruded elements the pin tools bounced because the pin tools contacted the radii 216A, 216B during welding. Moreover, the top flange 202 was thicker than the bottom flange 204 so the top flanges 202 of adjacent elements took much longer to weld so the top and bottom flanges 202, 204 of adjacent extruded elements could not be simultaneously welded. It was also discovered that simultaneously welding flanges with dissimilar thicknesses makes it difficult to control weld shrinkage and keep the finished bridge deck panel flat. Weld shrinkage is caused by heat generated during the friction-stir welding process. This required either the top flanges 202 or bottom flanges 204 to be welded first, and the extruded elements had to be flipped and rotated to start welding top flanges 202 or bottom flanges 204, depending on which were welded first.
Needless to say the process was not only time consuming, but potentially hazardous to laborers that fabricated the deck panel. The inventors of the subject invention have developed a deck panel and extruded aluminum elements that are much more cost effective in assemble. More specifically, the aluminum extruded elements have a profile that allows the extruded elements to be friction-stir welded much more efficiently and cost effectively.